Method for fluidizing solids



Nov. 19, 1957 A, A, GODEL 2,813,351

METHOD FOR FLUIDIZING SOLIDS Filed Sept. 25, 1955 METHOD FOR FLUIDIZING SOLIDS Albert Andr Godel, Paris, France, assignor to Compagnie Industrielle de Procedes et dApplications S. A. (C. I. P. A.), Fribourg, Switzerland, a corporation of Switzerland Application September 25, 1953, Serial No. 382,361 Claims priority, application France September 25, 1952 3 Claims. (Cl. 'S4- 10) This invention relates to lluidizing` solids, and more particularly to uidizing granulated solids normally resting upon a grid.

In the past, granulated solid particles have been fluidized by agitating such particles through the general turbulence produced by a continuous current of gas passing through a grid from bottom to top, without however, carrying the particles along with it. Such methods require a considerable volume of gas flow with relatively large power requirements for pumps or blowers.

I have now found that granulated solids maybe satisfactorily uidized, by employing a minimum quantity of gas with minimum power consumption, and without creating any excessive turbulence.

According to the invention, the granulated material is initially placed upon a stationary grid and a small quantity of gas is projected through the grid from below in successive pulsations of predetermined frequency and amplitude. A regular grading as to density and granular grading of the tluidized particles is thus obtained above the grid with a minimum requirement of fluidizing gas. The present invention is of marked advantage compared to known methods and apparatus in cases where it is desired to reduce to a minimum the flow of iluidizing gas without incurring blocking risks.

The word gas s employed in its broad sense to include air.

The invention is illustrated, very diagrammatically, in the accompanying drawings, in which- Fig. 1 is a diagrammatic elevation, partly in section and partly broken away, illustrating one form of the invention; and

Fig. 2 is a diagrammatic plan view showing one form of pulsation producer.

Referring now to Fig. l, the granular particles to be lluidized are placed upon a grid 10, above a gas ow or intake pipe 11, by means of which gas is projected through the grid with suitable pulsation. A pulsation producer 12 is connected in the gas ow or intake pipe 11 to create lluidizing pulsations of the gas passing through the grid 10, in a manner later to be described.

The grid is stationary and may comprise a number of forms.

The pulsation producer 12 may take various wellknown forms, as for example, vibrating plates, or a unit employing the exhaust gas of an internal combustion engine, or apparatus using the gas from vibrating burners, the explosion rate of which is especially regulated, or infrasonic or sonic generators, all too well-known to require specific illustration. In one contemplated ernbodiment an ordinary fan is employed in the gas flow pipe 11 and the pulsation producer takes the form of a pair of perforated screens 13 and 14, the screen 13 being fixed in position and the screen 14 lying immediately over the screen 13 and being oscillated, as by a rod 15 actuated by any suitable means 18, to bring perforations 16 therein into register and out of register with perforations 17 in the perforated plate 13. Such a pulsation ite States Patenti-O Mlce producer is illustrated in Fig. 2 of the drawings. Obviously the ordinary fan projects gas in but one direction; and according to the invention the perforated screen 14 is oscillated to bring the perforations 16 quickly into register with the perforations 17 in the perforated plate 13 and to move the perforations 16 slowly out of register with the perforations` 17.

Thus, a body of iluidized granulated solids is maintained above the grid 10 for use as may be required.

I have observed that when the iluidizing gas passing` through the grid according to the process of the present invention receives sharp impulses causing the instantaneous flow to vary, these impulses are reflected in the motion of all of the fluidized solid particles.` Furthermore, if such variations of instantaneous flow are periodical and continuous, the solid particles themselves are subjected to like periodical vibrations. Under the conditions stated above, the bed of iluidized solid material is far more regular than has heretofore been the case, without undesirable ebulition; and a considerable reduction of viscosity is observed,` which makes possible an easy flow of the material in all directions without blocking of the granulated material. This is so even though the average flow of the pulsating gas may be reduced by more than one-half.

The form of pulsations, their cadence and their amplitude may vary within wide limits according to the results to be achieved.

Without being limited to the particular steps of any process according to the invention, it may be stated that a preferred method consists of impressing upon the fluidizing current, impulses causing periodic reversals of flow of a frequency between 2 and 16,000 cycles per second.

Moreover, the aerodynamic suspension of the solid particles is greatly improved according to the process of the present invention by causing their instantaneous flow to vary during each cycle. In other words, the velocity of the iiuidizing gas current is varied according to a system wherein great acceleration is given the gas current during a brief time of increase of its instantaneous velocity, followed by a slower deceleration during a longer period of reduction of instantaneous velocity. Particularly advantageous results are attained when the acceleration time is less than 1/2 the deceleration time. It is even possible, by following the method of the present invention, to maintain solid particles in cornplete aerodynamic suspension, that is to say to fluidize the solid particles by means of an alternately ascending and descending gas current with but slight flow of the gas current, or even a net ow which is non-existent, provided the system of variation of instantaneous velocity during each cycle as set forth above admits of a sufficiently sharp acceleration and a suiciently slow deceleration, and also provided that the amplitude of the oscillation is sufficiently great. Of course, in this latter case, the grid should be a tight grid in order to prevent passage therethrough of the finest particles when they are in their momentarily descending vibrating period and reversely a tight grid is not necessary when the alternative current is only of the ascending type` The new method of fluidizing granulated particles forming the subject matter of the present invention is adapted for use for the usual purposes of iluidized solid particles, especially whenever it is desired to reduce to a minimum the tiow of gas necessary for fluidization, without such reduction, introducing blocking risks. Such is the case when gas and solids must be brought together in denite proportions to react chemically. Such is also the case when it is desired to effect air grading of iluidized material.

Finally, the novel method of the present invention may v. also be used to induce vertical or horizontal motion, by means of simple hydrostatic flow of the uidized mass. This is accomplished without bubbling and Without any` appreciable mixing of the luidized layers. Hence, the invention may be employed to effect methodical thermal exchanges between granulated solids moving in counter current, or between gas and solids circulating in a counter current of gas, or iinally for establishing methodical reactions of absorption and catalysis.

Thus in accordance with the present invention a saw tooth wave is imparted to the fluidizing gas, with the first half of the Wave representing the ascending pulsation being considerably shorter than the remaining portion of the Wave which constitutes the descending pulsation.

I claim:

1. The method of fluidizing solid particles, which comprises subjecting the particles to a fluidizing gas pulsating in the form of saw-tooth Waves, the rst half of each wave being a comparatively rapidly ascending pulsation during a comparatively short part of the period and the remaining portion of the wave being a cornparatively slower descending pulsation during the remainder of the period, the acceleration time being less than one-half of the deceleration time, said gas pulsating at a rate of between 2 to 16,000 cycles per second.

2. The method of uidizing. solid the particles located upon a grid to a uidizing gas pulsating in the form of saw-tooth waves, the rst half of each wave being `a comparatively rapidly ascending pulsation during a cdmparatively short part of the period and the remaining portion of the wave being a comparatively slower descending pulsation during the remainder of the period, the acceleration time being less than one-half of the deceleration time, said gas pulsating at a rate of between 2 to 16,000 cycles per second.

3. Themethod of fluidizingK4 solid the particles located upon aggrid tofa uidizing gas .projecting through the grid and pulsating in the form of saw-tooth waves, the first half of each wave being a comparatively rapidly ascending pulsation during a comparatively short part of the period andthe remaining portion of the wave being a comparatively slower descending pulsation during the remainder of the period, 'the acceleration time being less than one-half of the deceleration time, said gas pulsating at a rate of between 2 to, 16,000 cycles per second.

- References Cited in the le of this patent` rUNITED sTATEsPATENTs Morse et al. Feb. 2, 1954 

